[Amps] Henry Radio

[David Kirkby]

donii at sympatico.ca wrote:

> I heard the other day that many Magnetic Resonance medical devices use 
> tube type linears.
> Peter VE2FAR 

The Institute of Neurology in London <http://www.ion.ucl.ac.uk/>

has one of the largest MRI systems in the world. <http://www.ion.ucl.ac.uk/>

I can't recall the field strength, but there is *nothing* stronger in 
the world that can take a whole human body, although there is another of 
identical strength in the USA.  <http://www.ion.ucl.ac.uk/>

There are bigger MRI scanners that can take horses (with smaller field 
strengths), and smaller MRI scanners  (with larger field strengths, that 
can take small animals) but there is no bigger scanner for people. I 
don't know what the current spatial resolution of that system is, but 
last I knew they were achieving 0.3mm, which is limited by how still you 
can keep a human being. <http://www.ion.ucl.ac.uk/>

That scanner I know uses solid state amps. Here's the guy who heads the 
physics of the magnet
http://www.medphys.ucl.ac.uk/research-groups/mri_new/Roger%20Ordidge.htm#Position

I don't know the power of the amplifiers, but I do know they are solid 
state.

MRI is not my field of expertise, but I suspect new model will use solid 
state amps.

It's a bit of a shame really, as while hams can build big amps with one 
tube they find surplus, they are most unlikly to find a matched set of 
semiconductors on the surplus market.

The Pf^2R law will start to really hit hams at higher frequencies and 
powers.

I sometimes wonder if children will be able to build circuts as easily 
as I did as a kid (I'm 41). With most new ICs + semiconductors now only 
available in surface mount, it's not going to be as easy to build small 
projects. Wherease I could make my own PCB's as a kid, that is no longer 
going to be possible. And you need microscopes to assemble them.


-- 
Dr. David Kirkby, 
G8WRB

Please check out http://www.g8wrb.org/ 
of if you live in Essex http://www.southminster-branch-line.org.uk/